1. Field of the Invention
The present invention relates to a bottom bracket bearing assembly for a bicycle, and more particularly to a frame for easily mounting the chain wheel with a crank on it.
2. Prior Art
A conventional bottom bracket assembly as shown in FIG. 4A, includes an axle sleeve A, an axle A1, balls A2, ball seat A3 and nuts A4. All of those parts are mounted in a five-way tube A5, as shown in FIG. 4B. In practice, it has been found that the conventional assembly has some shortcomings. That assembly is difficult to mount, the parts easily loosen and fall out, due to the combination not sealing fully. Because of high accuracy required for the parts, the production and the assembly is difficult and unsuited for normal production.
Subsequently, a new axle frame with two flanges was developed to improve on the above-mentioned shortcomings. As shown in FIG. 5A, this second prior art assembly comprises an axle B, an axle sleeve B1, ball bearings B2, B3, flanged cup B4, adjusting cup B5, five-way tube B6 and ring B7. The assembly of those parts is shown in FIG. 5B. The axle B has two flanges B01 and B02 formed thereon, one of a bigger diameter and the other of a smaller diameter. In assembly, the larger diameter flange B01 is set in a caulking groove B11 of the axle sleeve B1, and the smaller flange B02 is set in a shaft bore B12 of the axle sleeve B1. Along with the other parts, the axle sleeve B1 is retained within five-way tube B6 for securing the axle B tightly in the combination and further for improving the mounting accuracy and reducing the production-cost of the assembly.
Therefore, the problems of the conventional bottom bracket bearing seem to be solved, but in practice, a new problem is found. One head of the axle B joins with an assembly of a crank and a chain wheel. Referring to FIGS. 5A and 5B, the two heads of the axle B are shown to be a reducing quadrangle, the continuation area between the reducing quadrangle and the cylindrical portion of the axle is formed by four tapers. The function of the quadrangle is to secure the assembly of the crank and the chain wheels, as shown in FIG. 6A. There are, however, some big problems associated therewith.
The chain wheels C are fastened on the crank D, and a through-hole D1 is formed in one end of the crank D for securement to the quadrangular head of the axle B. The assembly of the chain wheels C and the crank D is fastened on the axle B at the end of the quadrangular head, and the crank D is made of an alloy that is softer than the axle B. The through-hole D1 of the crank D is formed smaller than the axle B, and it is secured on the tapers of the axle B by a nut E from the end of said quadrangular head. But, corresponding to the different magnitude of force applied when tightening the nut E, the crank D is secured on the axle in different positions, to cause the base line of the chain wheels C to be out of alignment. That alignment error allows the chain to jump off the chain wheels C during running or when changing speed, which is one of the problems with that assembly.
A second problem results form the fact that the material of the crank D is softer than the axle's material. After pressing against the tapers for some time, the through-hole D1 of the crank D becomes enlarged to form a tapered hole from the side corresponding to the tapers of the axle, causing the chain wheels C to shake on the head of the axle B, as shown in FIG. 6A. Further, that condition may cause the chain wheels C to touch against the flanged cup B4 and cause damage.
Another problem is seen during repair of the assembly, as when the assembly of the crank D and the chain wheels C or the axle unit B fail and are taken apart from each other. During manufacture, the crank D is pressed on the axle B, the tapered hole of the through-hole D1 being pressed on the axle's tapers tightly. The through-hole D1 is thereby enlarged and when installed again it will axially approach the flanged cup. If the repairman uses excessive force during threading of the nut, or disassembly and mounting of the crank, many times, the chain wheels C will touch against the flanged cup on the axle B, as shown in FIG. 6B. Such contact blocks the rotation of crank D, causing damage to the crank D.